1. Field of the Invention
The present invention relates to a medical imaging diagnosis apparatus which detects an optimal scan timing for radiographing and collecting information on the inside of the body of a subject by use of a contrast medium.
2. Description of the Related Art
In current practice, when information on the inside of the body of a subject is radiographed, for example, by use of an X-ray CT (computed tomography) apparatus, a contrast medium is administered to an examination (or tomography) target region. The tomography using a contrast medium makes the geography of the target region appear sharper in contrast than any other region administered with no contrast medium.
In such tomography using a contrast medium, the contrast medium is administered not directly to an examination (or tomography) target region, but to a region other than the examination target region through intravenous injection or the like. After administering the contrast medium, the examination target region is radiographed by timing the arrival of the administered contrast medium at the examination target region.
The easiest way to observe the change in concentration of the contrast medium in the examination (or tomography) target region is to determine the change in concentration of the contrast medium by paying attention to blood vessels through which the contrast medium flows. With this taken into consideration, generally, the change in concentration of the contrast medium is observed in the blood vessels through which the contrast medium flows to the examination target region from the region in which the contrast medium has been administered. This is because the observation and determination is designed to be carried out by use of a property of the contrast medium which makes a region administered with the contrast medium appear sharper in contrast than any other region administered with no contrast region, in other words, by use of change in brightness (corresponding to change in CT values) on the display screen of the X-ray CT apparatus. In order to carry out such an observation, for instance, an examiner sets up an observation target region (hereinafter referred to as a “region of interest (ROI)”) in an appropriate blood vessel while checking on a fluoroscopic image generated, and radiographs the region (this type of radiography will be referred to as “scout scan” in contrast to “definitive scan” with which the examination target region is radiographed), thereby observing the change in concentration of the contrast medium in the region, as shown in Japanese Patent Application Publication Nos. Hei. 6-114049 (hereinafter referred as Document 1), Hei. 11-342125 (hereinafter referred to as Document 2) and 2004-113779 (hereinafter referred to as Document 3).
The time taken for the contrast medium to reach the examination target region after its administration varies depending on where the examination target region is. In addition, the time suitable for radiographing the examination target region is short. This makes it very difficult to evaluate whether or not the contrast medium has reached the examination target region. In some cases, for example, the target region may start to be radiographed before the contrast medium reaches the target region, or after the contrast medium has passed the target region.
For the purpose of preventing such a problem, Japanese Patent Application Publication No. 2005-245797 (hereinafter referred to as Document 4) discloses an X-ray CT apparatus including: a holder configured to hold an X-ray tube and an X-ray detector at their respective predetermined angles; a fluoroscopic image generator configured to generate a fluoroscopic image of the body of a subject taken in a predetermined direction on the basis of the dose of an X-ray beam which is continuously applied on the body of the subject from the X-ray tube thus held, and which is detected by the X-ray detector thus held; a display configured to display the fluoroscopic image thus generated; a determination unit configured to determine the start of a scan for tomography on the basis of change in concentration of a contrast medium in the fluoroscopic image.
Use of the X-ray CT apparatus of this type is considered to make it possible to obtain a tomographic image appropriately highlighting the geography of the predetermined region, and to reduce the radiation exposure dose on the body of the subject in comparison with the current practice using a pre-scan in the real prep scan method.
As to Documents 1, 2 and 4, however, it is considered to be difficult to observe the change in concentration of the contrast medium in the fluoroscopic image in determination of the start of a scan for tomography.
That is because only a single ROI is set up to observe the change in concentration of the contrast medium. This sometimes makes it difficult for even a skilled examiner to set up an ROI in an exact position on a blood vessel to be observed. If an ROI is not successfully set up on the blood vessel, for instance, when the ROI is unsuccessfully set up on a bone, it is impossible to observe the change in concentration. As a result, the examination target region is not appropriately radiographed. Depending on where the examination target region is, a blood vessel suitable for observing the change in the concentration is not always found. Moreover, in some cases, it is difficult to find an image representing blood vessels in the generated fluoroscopic image. In these cases, it is impossible even to set up an ROI.
According to Document 3, multiple ROIs are set up. The multiple ROIs are set up because a CT value of image data needs to be measured by means of a first low-dose X-ray scan (or a first scan), a high-dose X-ray scan (or a second scan) and a second low-dose X-ray scan (or a third scan) for the purpose of determining the timings of the start and end of a high-dose X-ray scan in the contract-enhanced dynamic CT. This makes it possible to grasp the start timing and the like with high exactness. On the other hand, this requires much labor and time. For this reason, it is impossible to easily set the start timing and the like.
The present invention has been made for the purpose of solving the above problems. An object of the present invention is to provide a medical imaging diagnosis apparatus capable of, when change in concentration of a contrast medium is observed prior to radiographing and collecting information on the inside of a body of a subject by using the contrast medium, more easily specifying a region including a blood vessel suitable for the observation of the change in concentration of the contrast medium, and thus of increasing the diagnosis efficiency, as well as of informing an operator of the optimal timing to scan an examination target region on the basis of the change in concentration in the region.